The invention relates to a method and an arrangement for operating an internal combustion engine and especially an engine having gasoline direct injection.
The demands imposed on a modern internal combustion engine with respect to a reduction of the fuel consumption and a reduction of the discharged toxic substances become ever greater. The electronic control of the internal combustion engine must operate with ever greater accuracy to satisfy these requirements. This applies especially to the control of the following: the fuel mass to be injected, the ignition angle to be adjusted and/or the air charge to be metered. Especially the quantity, which represents the load of the engine, must be accurately determined because this quantity is applied to compute the control quantities. The most suitable quantity to represent the load is the air charge, especially the relative air charge of the cylinders per stroke. This quantity is a quantity, which is proportional to he fresh air, and a very high accuracy of the engine control can be achieved when using this quantity to determine the control quantities. The air charge is computed in the most accurate way possible from the available quantities. This is described, for example, in U.S. Pat. No. 6,422,202 for an air-mass controlled control system.
This U.S. Pat. No. 6,422,202 is incorporated herein by reference and presents a procedure for computing the relative air charge rl which is determined in accordance with an intake manifold model from a signal of an air-mass sensor. Furthermore, the computation of the air charge signal from the throttle flap position is shown in this patent application as an alternative. Here, intake manifold pressure signals and ambient pressure signals as well as various corrective factors are used. With the aid of these signals, the air mass signal or air charge signal, which is computed on the basis of the throttle flap angle, is adapted to the signal which was determined on the basis of the measuring signal of the air mass sensor and which is per se more accurate.
The driver or other control units, such as a transmission control unit, present a specific torque request to the engine control. The torque request is converted into a desired air charge in the combustion chamber. From this, the charge control computes a desired value for the throttle flap position which is adjusted by means of a position controller. Characteristic quantities of the throttle flap system are used in the computation of the throttle flap desired value. The intake manifold pressure sensor or the air mass sensor measures an actual charge which deviates from the desired charge when the actual characteristic quantities deviate from the quantities stored in the control unit. The requested torque is not set. In the adaptation, the charge, which is computed on the basis of the throttle flap angle and rpm, is compared to the charge computed on the basis of the air mass sensor signal. Then there are deviations, the adaptation changes the characteristic quantities of the throttle flap system so long until the two charges are coincident. These changed characteristic quantities of the throttle flap system are considered in the control of the charge. With the changed characteristic quantities, a changed throttle flap position desired value results to the same torque command and the same desired charge. With this other throttle flap desired value, a charge adjusts, which is measured by the air mass sensor and which is coincident with the desired value. The requested torque is adjusted. The same applies to the EGR system. Here too, the desired EGR desired rates are only reached with calibrated characteristic quantities of the system.
A procedure is disclosed in German patent publication 197 53 873 in accordance with which, and without use or an air mass sensor, the relative air charge for controlling the engine is determined on the basis of the measured intake manifold pressure while considering the internal and external exhaust-gas recirculation.
With respect to an exhaust-gas recirculation system, international patent application PCT/DE 01/00200, filed Jan. 18, 2001, is incorporated herein by reference and discloses a procedure for determining the partial pressure of an external exhaust-gas recirculation. The partial pressure determined in this manner is evaluated to determine an intake manifold pressure value. The model used here is adapted to the actually measured intake manifold pressure. An increase and/or an offset of a characteristic line, which defines the air mass flow through the exhaust-gas valve in dependence upon the position thereof, is corrected so that the measured intake manifold pressure and the model intake manifold pressure, which is formed on the basis of the partial pressures, are coincident.
An optimal accuracy of the computation of the air charge in the combustion chamber is therefore achieved with systems wherein an air mass sensor, an intake manifold pressure sensor and a throttle flap angle sensor are used for load detection. This permits to adapt the determination of the air charge or air sass flow on the basis of the throttle flap angle (which is inaccurate) to the charge quantity or mass flow quantity, which is determined on the basis of the air mass sensor, by means or corrective factors and to control the charge with the accuracy of the air mass sensor signal. The charge quantity or mass flow quantity is determined on the basis of the air mass sensor. In addition, the use of both signals improves the adaptation and determination of the external exhaust-gas recirculation rate (residual gas charge) whose computational determination can likewise be burdened with inaccuracies.
However, if the air mass sensor is not used, for examples because of reasons of cost or in the case of a fault and, in lieu thereof, an intake manifold pressure sensor is utilized as the main charge sensor, then the adaptation of the throttle flap system and/or the exhaust-gas recirculation system to the main charge sensor should be achieved to thereby maintain the accuracy of the load detection.
With the adaptation of a charge detection, which is based on the throttle flap position, to the accuracy of a charge detection based on the intake manifold pressure sensor, it is possible, notwithstanding the omission of the air mass sensor, to make available a charge detection satisfying the accuracy requirements. Notwithstanding the omission of the air mass sensor, the possibility of an adaptation is thereby retained.
It is especially advantageous that an adaptation is also possible for the adaptation of the exhaust-gas recirculation system.
It is especially advantageous that the adaptation result can be evaluated for monitoring the exhaust-gas recirculation system.
By adapting the charge detection, which is based on the throttle flap angle, to the charge detection, which is based on the intake manifold pressure sensor, a precise control of the engine is made possible and the throttle flap and/or the exhaust-gas recirculation valve is so driven that the desired air charge and/or the desired residual gas charge coincides with the actual air charge, which is computed via the intake manifold pressure sensor, and/or the actual residual gas charge.
An improvement of the accuracy of the adaptation is achieved by utilizing an ambient pressure sensor. However, this sensor can be omitted when the tolerance, which is expanded thereby, is adequate for the accuracy of the engine control.
In an advantageous manner, an improvement of the accuracy of the charge detection is achieved when the adaptation of the charge, which is based on the throttle flap angle, to the charge, which is based on the intake manifold pressure, takes place only under specific peripheral conditions especially when the exhaust-gas recirculation valve is closed, that is, a possibly present exhaust-gas recirculation is inactive.
If the ambient pressure sensor is not used, then the multiplicative adaptation factor defines, for an inactive exhaust-gas recirculation, a quantity which represents the ambient pressure and which is evaluated when detecting the charge and/or for the control of the engine.